OBJECTIVETo analyze epidemiological characteristics of norovirus variant of GII.4 Sydney from January 2012 to June 2014 in sentinel hospitals of Guangdong province, as well as the outbreaks caused by norovirus variant of GII.4 Sydney.

METHODSDuring January 2012 to June 2014, a total of 10 750 fecal samples were obtained from 22 hospitals of surveillance sites in Guangdong province. Those samples were sent to the local municipal CDCs for extracting and detecting norovirus nucleic acid. Then, all the positive samples were delivered to Guangdong provincial CDC that used Random Number Method to draw 855 positive samples for norovirus genotyping, and 690 samples were successfully sequenced. Chi-square tests were used to compare norovirus infection status of diarrhea cases in different age groups as well as during different periods. Epidemiological data of 13 outbreaks which were caused by norovirus variant of GII.4 Sydney from January 2012 to June 2014 were collected from the Public Health Emergency Management Information System of Guangdong Province, and the epidemiological characteristics were analyzed.

RESULTSThe norovirus variant of GII.4 Sydney was first detected in August 2012 and the detection rate was 13/15 in November 2012. During November 2012 to January 2013 (period T1), the norovirus positive rate of each month was 23.8% (100/421), 15.9% (61/383) and 19.2% (95/495), respectively. During November 2013 to January 2014 (period T2), the norovirus positive rate of each month was 17.0% (90/529), 8.7% (37/426) and 11.2% (46/409), respectively which were significantly lower than that of period T1 (χ² alue was 6.65, 9.93 and 10.74. P value was 0.010, 0.002, and 0.001, respectively). In period T1, the norovirus positive rate of people ages 15 and older was 26.3% (143/543) and the rate of people under 15 was 14.9% (113/756) (χ² = 2.90, P < 0.001). In period T2, the norovirus positive rate of people ages 15 and older was 10.1% (52/516) and the rate of people under 15 (14.3% (121/848)) (χ²= 5.09, P = 0.024). The foodborne transmission was the infection source for ten of thirteen outbreaks.

CONCLUSIONThe norovirus variant of GII.4 Sydney was first detected in August 2012. The epidemic began to occur in the community since November 2012, and the strength of the epidemic declined 1 year later. The foodborne transmission was the main infection sources for the outbreaks caused by norovirus variant of GII.4 Sydney.